This invention concerns a process for the preparation of a liquid crystalline polymer film by feeding a film of molten liquid crystalline polymer to rollers which oscillate along their axes with respect to another and whose surfaces are preferably slightly embossed, and wherein the temperature of the rollers is such that the film solidifies on one roller and forms a molten bead on the other roller. The resulting films have improved transverse direction properties.
Thermotropic liquid crystalline polymers (LCPs) are important items of commerce, being useful as molding resins, for films, and for coatings. The most common method of forming films from thermoplastics is extrusion of the polymer through a film die. When this is done with LCPs, the polymer usually is highly oriented in the machine (extrusion) direction (MD), and is quite weak and brittle in the transverse direction (TD). Special methods have been developed to produce LCP films (or thin tubes which can be slit into films) with more balanced MD/TD properties, thus improving the TD properties of the film. However, such methods, which for instance are described in U.S. Pat. Nos. 4,384,016, 4,820,466, 4,963,428, 4,966,807, 5,156,785, 5,248,305,288,529, 5,312,238, and 5,326,245 and G. W. Farrell, et al., Journal of Polymer Engineering, vol. 6, p. 263-289 (1986), usually require the use of intricate, expensive equipment which may be difficult to operate reliably, produce tubes which may not lay flat as films, and/or require labor intensive lay-up methods. One of these methods is moving in the TD an extrusion die surface which contacts the molten LCP. Thus better methods of preparing improved LCP films are needed.
This invention concerns, a process for the production of a final thermotropic liquid crystalline polymer film, comprising, feeding a first film of a molten thermotropic liquid crystalline polymer to a pair of rollers which have a gap between them which is approximately equal to a thickness of said first film, and passing said molten thermotropic liquid crystalline polymer through said gap, provided that:
said rollers oscillate relative to one another and parallel to their rotational axes at a frequency of about 20 to about 200 Hz;
said rollers are at such a temperature or temperatures that said thermotropic liquid crystalline polymer freezes against one roller, and on the other roller a rolling bank of molten thermotropic liquid crystalline polymer is formed;
and provided that said temperature or temperatures and said frequency is such that said thermotropic liquid crystalline polymer is further oriented in a transverse direction.
This invention also concerns an apparatus, comprising, two rollers with a gap between them, said rollers rotating in opposite directions, each of said rollers having an axis of rotation, and said rollers oscillating in opposite directions with respect to one another along their respective axes of rotation at a frequency of about 20 to about 200 Hz.